The present invention relates to a process for the metathesis of olefins using an improved catalyst with a rhenium base.
The metathesis of olefins, or reaction redistributing alkylidene groups, is very useful in practice, e.g. for re-balancing the light olefins which result from steam cracking, olefins such as ethylene, propylene and butenes.
Various types of catalysts are capable of being used in the metathesis reaction: either homogeneous ones with constituent elements which are all soluble in the reaction medium, or heterogeneous ones which at least one element which is insoluble in said medium. These latter are particularly worthwhile when the active metal is costly and when it is necessary to envisage its reuse without any waste. This is the case for catalysts with a rhenium base, use of which in heterogeneous form has been recommended for catalysing the metathesis of simple olefins, e.g. in U.S. Pat. Nos. 3,641,189 and 3,676,520.
These catalysts have been prepared in the prior art by introducing rhenium oxide, using methods conventional in heterogeneous catalysis, onto various supports as described in U.S. Pat. No. 3,642,931. for example. Of the various supports, alumina, or a support containing alumina, seems to have the most worthwhile properties for conferring good activity and good stability upon the catalyst.
Numerous modifications to the base catalyst constituted by rhenium on alumina have been described to improve its properties. Beneficial effects have thus been found by adding alkaline compounds or alkaline earth compounds (U.S. Pat. No. 3,594,440, U.S. Pat. No. 3,637,892), acid anions (U.S. Pat. No. 3,697,613), tin oxides (GB 1,377,161), boron oxide (U.S. Pat. No. 5,055,628), or rare earths elements (U.S. Pat. No. 3,728,414).